Process of regaining tin.



llnrrno dramas PATENT @rrrcn PAUL BERGSOE, OF COPENHAGEN, DENMARK.

PROCESS OF REGAINlNG TIN.

SPECIEECATIQN forming part of Letters Patent No. 691,101, dated January 14, 1902.

Application filed May 10,1900v To all whom it may concern:

Be it known that I, PAUL BERGSOE, a subject of the King of Denmark, risiding in Copenhagen, Denmark, have invented certain new and useful Improvements in Processes of Regaining Tin, of which the following is a specification.

This invention relates to processes of refining or regaining metallic tin in a pure state from its alloyssuch as Britannia metal, antifriction metal, and metal Waste or scrap-- and from objects coated with tin or tin alloys, such as tinned sheet-iron and soldered metal; also, for the refining of raw tin.

The object of the invention is to provide a simple, economical, and effective process of this nature capable of practical and continuous operation upon a large scale; and theinvent-ion consists for this purpose of the process herein described of regaining tin, which comprises the steps of subjecting a tin-bearing material to the action of a stannic'salt solution, subjecting the resulting stannous-salt solution in the presence of a cathode and an indifferent anode to electrolysis, and thereafter continuously subjecting said solution alternately to contact with a tin-bearing material and to electrolysis in the presence of a cathode and an indilferent anode.

Before subjecting the raw tin-bearing material to the process it is preferable to clean or otherwise preliminarily prepare the same. Tinned sheet-iron waste may, however, be treated directly without any previous clean- J ing,comminution,orsorting. Tinalloyshave to be first rendered in suitable condition for solution by granulation or by casting the same into thin sheets, the object being to expose a large surface to the action of the solvent fluid in carrying on the process.

The process consists, essentially, of two stagesfirst, the step of dissolving tin from a material bearing the same, whereby the tin of a suitable stannic combination contained in the solvent liquid is caused to change its form or valency from four to two-in other words, from a teravalent to a divalent stateso that the solution becomes stannous in charactor, and, secondly, an electrolytical deposition step, wherebya quantity of the tin from the stannous solution formed in the first step Serial No. 16,14 5. (No specimens.)

is removed in a pure state and simultaneouslyan equivalent quantity of tin in combination in the liquid is transformed from a divalent to teravalent condition, whereby the solvent liquid is reformed.

The solvent liquid may consist of an aqueous solution of a stannic salt-for instance, of stannic chlorid orofanyothersimilarly-acting stannic compound. Indifferent salts for increasing the conductive capacity of the liquid may be added.

The dissolving step of the process and the electrolytical step of the same may be carried out in the same vessel; but in practice it is preferable to allow them to take place simultaneously in separate vessels, which communicate, however, with each other, so that the liquid can circulate between them. When the stannons solution is allowed to flow contin nously from the solution vessel to the electrolytic cells and the stannic solution from the latter back to the solution vessel, and so on, an uninterrupted transport of tin from the raw material in the solution vessel to the cathodes in the electrolytic cells is obtained without the raw material itself forming an electrode.

The following formulae, wherein Rindlicates the anionsuch, for example, as chlorinindicate the reactions of the process:

It will be seen that this process differs from the ordinary electrolysis, wherein the anion either combines direct with the metal of the anode or evolves into a free gaseous form, or, lastly, gives rise to a secondary evolution of oxygen.

It is essential to the carrying on of myimproved process that an anode of inert or indifferent material, such as carbon, be used. Plates of tin, iron, or the like may be employed as cathodes. By the electrolytical step there is directly formed a tin compound of tetravalent form. That the anion is not first evolved in aeriform condition and. later on combines with the neighboring tin ions will be seen from the circumstance that the electrolysis takes place at a considerably lower potential than if gas had been evolved. It

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is a necessary condition in order to carry on the process in accordance with the abovecited formulee that a current of low potentialt'. e., about 1.5 to 1.7 voltsand an electrolyte containing a sufficient quantity of divalent tin, or, in other words, not too concentrated as regards its contents of tetravalent tin, be employed. A sufiicient quantity of tin must always be contained in the solution vessel for absorption by the solvent fluid, so that the same can always take up without interruption any quantity demanded to replace that which has been deposited. The process will remain continuous while this condition exists. When the white color of the tin upon the tin-scrap or other material disappears, it is an indication that an additional supply of material should be put into the vessel. The tin is deposited on the cathodes in compact metallic form. The raw material does not itself enter into the circuit or serve as an anode. Acid-baths can be used without incurring the danger of introducing foreign metals into the tin deposited on the cathodes. The tin obtained by this process, in contradistinction to spongy tin, can be melted down without loss. The tin is perfectly pure, furthermore, because any foreign metals, such as zinc, which may have been dissolved during the dissolving of the raw material are not deposited by the electrolysis and not even a trace of them is found in the tin.

The stannic compounds-such, for instance, as stannic chlorid, (H SnCl )which were heretefore not employed in a process of this kind are powerful reagents, acting in the nature of oxidizing-acids, and their employment renders the process an entirely practical, continuous, and economical one.

Having thus described my invention, I claim as new and desire to secure by Letters Patent- 1. The herein-described process of regaining tin, which consists in subjecting a tin-bearing material to the action of a stannic-salt solution, bringing the resulting stannous solution into contact with a cathode, and with an anode of indifferent material, and passing an electric current through said solution between said anode and cathode, substantially as set forth.

' 2. The herein-described process of regaining tin, which consists in subjecting a tin-bearing material to the action of a stannic-salt solution, bringing the resulting stannous-salt solution into contact with a cathode and with an anode of indifferent material, passing an electric current through said solution between said anode and cathode, whereby metallic tin is deposited upon the cathode and the solution converted into a stannic-salt solution, and thereafter continuously subjecting said solution alternately to contact with a tin-bearing material and to electrolysis in the presence of a cathode and an indiiferent anode, substantially as set forth.

In testimony that I claim the foregoing as my invention, I have signed my name in presence of the subscribing witnesses.

PAUL BERGSOE.

Witnesses:

ERNEST BOUTARD, L. HOFMAN BANG, J. C. JAooBsEN. 

